Nathalie is an Alien Buster, a member of a team that kills aliens in the Adkad City on Planet Zelea- home for humans after Earth's destruction. Haunted by her parents' death in the field, she joined the Alien Busters Institute in order to carry on their legacy. While on a mission, she discovers an alien baby. How can she kill this enemy when she's formed a strong attachment, even if it's forbidden?